Distance Vector

Routers use distance vector–based routing protocols to periodically advertise the routes in their routing tables. Routing information exchanged between typical distance vector–based routers is unsynchronized and unacknowledged. Table 1.1 lists some distance vector–based routing protocols.

Table 1.1 Distance Vector–Based Routing Protocols

Advantages of Distance Vector–Based Routing Protocols

• Simpler.

  Distance vector–based routing protocols are simple router advertisement processes that are easy to understand.

• Easy to configure.

  In its simplest incarnation, configuring a distance vector–based routing protocol is as easy as enabling it on the router interfaces.

Disadvantages of Distance Vector–Based Routing Protocols

• Large routing tables.

  Multiple routes to a given network ID can be reflected as multiple entries in the routing table. In a large internetwork with multiple paths, the routing table can have hundreds or thousands of entries.

• High network traffic overhead.

  Route advertising is done periodically even after the internetwork has converged.

• Does not scale.

  Between the size of the routing table and the high overhead, distance vector–based routing protocols do not scale well to large and very large internetworks.

• High convergence time.

  Due to the unsynchronized and unacknowledged way that distance vector information is exchanged, convergence of the internetwork can take several minutes. While converging, routing loops and black holes can occur.

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